Genesis 2:24

24.Therefore shall a man leave It is doubted whether Moses here introduces God as speaking, or continues the discourse of Adam, or, indeed, has added this, in virtue of his office as teacher, in his own person. (151) The last of these is that which I most approve. Therefore, after he has related historically what God had done, he also demonstrates the end of the divine institution. The sum of the whole is, that among the offices pertaining to human society, this is the principal, and as it were the most sacred, that a man should cleave unto his wife. And he amplifies this by a superadded comparison, that the husband ought to prefer his wife to his father. But the father is said to be left not because marriage severs sons from their fathers, or dispenses with other ties of nature, for in this way God would be acting contrary to himself. While, however, the piety of the son towards his father is to be most assiduously cultivated and ought in itself to be deemed inviolable and sacred, yet Moses so speaks of marriage as to show that it is less lawful to desert a wife than parents. Therefore, they who, for slight causes, rashly allow of divorces, violate, in one single particular, all the laws of nature, and reduce them to nothing. If we should make it a point of conscience not to separate a father from his son, it is a still greater wickedness to dissolve the bond which God has preferred to all others.

They shall be one flesh (152) Although the ancient Latin interpreter has translated the passage ‘in one flesh,’ yet the Greek interpreters have expressed it more forcibly: ‘They two shall be into one flesh,’ and thus Christ cites the place in Matthew 19:5. But though here no mention is made of two, yet there is no ambiguity in the sense; for Moses had not said that God has assigned many wives, but only one to one man; and in the general direction given, he had put the wife in the singular number. It remains, therefore, that the conjugal bond subsists between two persons only, whence it easily appears, that nothing is less accordant with the divine institution than polygamy. Now, when Christ, in censuring the voluntary divorces of the Jews, adduces as his reason for doing it, that ‘it was not so in the beginning,’ (Matthew 19:5,) he certainly commands this institution to be observed as a perpetual rule of conduct. To the same point also Malachi recalls the Jews of his own time:

‘Did he not make them one from the beginning? and yet the Spirit was abounding in him.’ (153) (Malachi 2:15.)

Wherefore, there is no doubt that polygamy is a corruption of legitimate marriage.